1. Field of the Invention
The present invention relates generally to vertical takeoff and landing aircraft and, more particularly, to such aircraft which derive aerodynamic lift and thrust from opposed rotatable paddle wheel assemblies of airfoil-shaped blades in place of the wings and propellers or jet engines of a conventional airplane.
2. Description of the Prior Art
The history of the aircraft industry has been marked with innovations that have contributed in varying measure to the development of the present day aircraft, with each innovation recognizing or anticipating a changing need as ground transport gradually gave way to air transport. Early innovations in this development were directed to the range, speed and cargo capacity of the aircraft, with later innovations aimed at improved maneuverability and lift as aircraft size and weight increased and as urban areas mushroomed to lessen the adequacy of the city based airport.
With the obsolescence of the city-based airport, new airports of more adequate acreage were established in areas remote from the cities, at distances ranging from 10 to 50 miles and frequently necessitating more land travel time than flight time. Although aircraft accessibility was improved with the advent of air shuttle and land limousine services, the latter have provided but slight reductions in land travel time, and air shuttle service has remained generally out of the financial reach of the general public for use on a regular basis. With the advent of today's giant sized aircraft, even the remote area airports have required expansion, with runways being lengthened to satisfy their take off and landing requirements.
In recognition of the lift limitations of fixed wing aircraft and the cargo limitations of the helicopter, further innovation is required if present airport patterns are to be altered, with remote area airports ever expanding to accommodate commercial aircraft, and with city airports remaining the exclusive property of private and small commercial aircraft and helicopters.
In recent years, there has been more and more interest in the development of vertical takeoff and landing cargo and passenger carrying aircraft that have the capability of taking off and landing on either the shorter runways of the city airport or the longer runways of remote area airports, thereby preserving the utility of existing airports while at the same time bringing the ultimate destination of the traveler within more accessible and convenient reach, with land travel time reduced to its former more proportionate ratio. Tilt wing and tilt rotor concepts have generated particular interest as design compromises that have the vertical takeoff and landing advantages of the helicopter and approach the speed and range capability of conventional fixed wing aircraft. Such concepts have significant military potential as well as commercial.
In U.S. Pat. No. 1,754,977 to Bergman, an airplane is provided with rotatable assemblies of impeller blades having the shape of an inverted trough. As the impeller blades are rotated, shutter vanes pivotably suspended on each blade are opened or closed by air pressure to provide lift and thrust when closed, and to minimize drag when opened. The position of each impeller blade relative to its supporting assembly is controlled by a control eccentric to provide for vertical and horizontal motion of the aircraft.
In U.S. Pat. No. 2,123,916 to Rohrbach, an aircraft is provided with revolving assemblies of wings. The angle of incidence of the revolving wings is said to be controlled to the aerodynamically correct position relative to the incident airflow for all wing positions by an oscillation gear mechanism for all flight conditions.
In British Patent No. 480,750, a cyclogyro aircraft is provided with rotor assemblies each having a plurality of vanes distributed around the rotor axis. As the rotor rotates, the vanes are constrained to rotate relative to the rotor by an eccentric gear mechanism or, in another embodiment, a cam slot and pin follower, so that each vane is maintained at a substantially constant angle of attack relative to the resultant airstream. The gear or cam mechanism is adjustable to vary the phase, or angular disposition, of the vanes relative to the aircraft fuselage.
In U.S. Pat. 2,507,657 to Wiessler, an aircraft is equipped with rotors of pivotably mounted blades which operate in paddle wheel fashion. The cyclic variation of incidence of the blades and their initial relative inclination are controlled by supports which are journaled in a fixed axis. The fixed axis is slotted so that it may be positioned eccentrically relative to the rotor shaft. Screw mechanisms driven by motors vary the eccentricity of the fixed axis. The rotors may be held in fixed position when sufficient airspeed is attained, so that the blades act as conventional wings.
In U.S. Pat. No. 2,413,460 to Main, an airplane is provided with conventional wings and rotatable Cycloidal propellers disposed beneath the wings. Each propeller comprises an assembly of blades which are pivotably connected to spokes of the propeller. As the propeller rotates, the angles of incidence of the pivotably connected blades are controlled by a cam, roller, and linkage mechanism.
In U.S. Pat. No. 2,580,428 to Heuver, a cycloidal rotor for aircraft is described. The rotor provides lift and thrust as the rotor is rotated by the cycloidal motion of a series of airfoil members or blades relative to the rotor. Control of the airfoil motion, or pitch, is accomplished through a system of sprocket wheels, gear trains, linkages, eccentric pins, and levers.
In one interesting development disclosed in U.S. Pat. No. 4,210,299 to Chabonat, an aircraft is provided with a propulsion and lifting rotor comprising two diametrically opposed wings of aerofoil section located at respective sides of a fuselage at right angles to the rotor axis. Each of the wings is mounted for pivotal movement about a respective axis spaced from the axis of the rotor and lying parallel to the leading edge of the wing.
In one embodiment, a cam mechanism changes the angle of incidence of the blades both collectively and cyclicly. The cam preferably forms part of a set of cams keyed slidably on the cam shaft. By displacing the set of cams, it is possible to modify the pattern of incidence variation as a function of the speed of flight.
In another development, as disclosed in U.S. Pat. No. 4,194,707 to Sharpe, an aircraft is provided with rotor assemblies on opposite sides of its flight axis. The vanes on the rotor assemblies are each individually pivoted by means of a complex linkage system so that the rotor vanes can be pivoted in one direction to draw air into the rotor assembly while the vanes are in communication with the air above the aircraft and can be pivoted in the opposite direction to discharge air from within the rotor assembly while the vanes are in communication with the air below the aircraft to exert lift on the aircraft. The vanes on both the rotor assemblies can be simultaneously oriented in the same sense and degree of pivoting or can be pivoted in the opposite sense. This allows the rotor assemblies to be selectively controlled so as to give the aircraft a vertical takeoff and landing capability.
U.S. Pat. No. 4,482,110 to Crimmens, Jr., describes a composite aircraft in which a system of wing and blade airfoils rotate about the horizontal longitudinal axis of a lighter-than-air gas containment bag to provide lift and thrust for augmenting or opposing the aerostatic lift forces of the gas containment bag. Engines mounted on the airfoil components rotate the wing and blade airfoils and gas containment bag about the longitudinal axis of the gas containment bag. Each wing airfoil and engine assembly are rotatably mounted on a structural support, their rotation being controlled by a system of cylinders, pulleys, and cables such that, in forward flight when the cyclorotor does not rotate, the wings can be rotated to a point where the spanwise axis of the wings is perpendicular to the horizontal axis of the aircraft and thus provide lift in the manner normal to fixed wing aircraft. The angle of attack of each wing is further controlled by a system of cylinders, pulleys, and cables which rotate each wing about its spanwise axis. The angle of attack of the blade airfoils is also controlled by a system of cylinders, pulleys, and cables to rotate the blades about their spanwise axes, so that the blades provide propeller-like thrust for forward or rearward movement of the composite aircraft.
The positions of the wing and blade airfoils are controlled through an electronic control system which accepts input commands from the pilot, or a remote control operator, or an autopilot, and also input data as to aircraft altitude, attitude, heading, and ground relative positions, and generates cyclic and collective control signals for servo control of blade and wing airfoil positions.
And, in U.S. Pat. No. 5,100,080 to Servanty, a rotor for developing lift and propulsive forces for an aircraft is disclosed. The rotor comprises several rotatable profiled blades. The angle of incidence of each blade is controlled in real time as a function of the angular position of the blade in the rotor's rotation cycle and the flight conditions of the aircraft to produce the optimum lift and propulsion forces from each blade for the then-existing flight conditions.
In Servanty, a computational device is used to store physical configuration information about the rotor and blades, to measure and determine at each instant the aerodynamic conditions governing the production of lift and thrust by the blades and also the azimuthal position of each profiled blade, to generate control signals representative of the lift and drag forces desired for a particular flight condition, and to calculate the instantaneous geometric angle required for each blade as a function of the aforementioned stored parameters, determined values, and control signals. Control means are provided to position each blade at each instant to the instantaneous geometric angle calculated for that blade.
The movement of each profiled blade is obtained by combining an average movement, or cyclic angle of incidence, and a complementary movement, or additional angle of incidence. The average movement is produced by a "kinematic chain" which is common to the set of profiled blades and has a mechanical structure corresponding to the particular "law" chosen for the average movement, as for example a circular translation of each blade during one revolution of the rotor.
The "kinematic chain" comprises a flange connected to the rotor shaft, which supports the body of a rotary hydraulic actuator associated with each profiled blade, and a toothed wheel centered on the rotor shaft, which is coupled to a mechanical phase shifter and drives the bodies of the rotary hydraulic actuators as the rotor revolves to rotate the profiled blades according to the selected average cyclic "law" of incidence.
The complementary movement is obtained by a hydraulic system, powered by rotation of the rotor, which includes distributors and servo valves associated with each rotary actuator to provide hydraulic power to that actuator to generate the complementary movement in response to control signals from the calculating means.
In Servanty, the mechanical structure and configuration of the kinematic chain are defined by the particular cyclical variation of blade angle selected, and cannot be changed without massive redesign of the kinematic chain. Although the invention of Servanty thus provides for a relatively reduced amplitude of movement of the rotary actuators, it precludes operational flexibility of the rotor to adapt to conditions where other patterns of cyclic variation would be more effective for a particular flight condition, or where no pattern of cyclic variation is required for optimum performance. Additionally, the invention of Servanty requires a more complex implementation of the instantaneous blade geometric angle , .PSI., than the present invention since the angle is achieved by combining the average and complementary movements discussed above, rather than directly.
While the basic concepts presented in the aforesaid patents are desirable, the mechanisms employed to effect their operation are far too complicated to render them practical, have limited or no flexibility to adapt to differing flight conditions, and the extent of control achieved is minimal. It was in light of the prior art as just discussed that the present invention has been conceived. In short, it is an object of the present invention to provide an aircraft having the cargo capacity of the modern fixed wing aircraft and a lift comparable to the helicopter, such that existing city based and remote area airports may be utilized for vertical landings and takeoffs, enabling the traveler to embark and disembark in closer proximity to his or her home and destination. It is a further object of the present invention to provide such an aircraft in which cyclic variations of the individual blades of the paddle wheel assemblies of the aircraft are optimized for each flight condition and pilot command, and in which the blades are pivoted to their respective optimum angle of incidence by a system of controlled linear actuators which is more flexible and adaptable to differing flight conditions than the cam and gear mechanisms of the prior art.